Changed the WordPress theme and thumbnails broke? Product images cropped at the edges, gallery looks like a random set of pixels, and the WooCommerce storefront resembles a funhouse mirror. A familiar situation for anyone who has gone through a redesign.

The issue is in WordPress mechanics: the theme registers thumbnail sizes via add_image_size(), but these sizes apply only to new uploads. Old images remain in their previous proportions. Manually re-uploading hundreds of files is a road to nowhere.

Regeneration plugins go through the media library, delete outdated thumbnails and create new ones according to current settings. Six tools in this collection cover tasks from simple size updates to full conversion to WebP and AVIF. Choose based on your scenario.

💡 Quick overview:

• Identify registered thumbnail sizes via Settings → Media or a plugin like Simple Image Sizes, this is the foundation without which it's unclear what to regenerate
• Choose a tool for the task: simple regeneration after a theme change, forced regeneration with deletion of old files, or comprehensive optimization with format conversion
• Make a full backup of files and database, regeneration physically overwrites thumbnails on disk, and an interrupted process leaves visual chaos
• Run regeneration for all images at once or selectively by post types, individual images, or date ranges

Comparison table

1. Regenerate Thumbnails

A classic from Alex Mills. Over a million active installations and 395 reviews on WordPress.org, the very plugin people install first when changing themes. After the author's departure in 2019, it's maintained by the community, latest version 3.1.6, tested on WordPress 6.8.5.

Go to Tools → Regenerate Thumbnails, select images and start the process. The plugin goes through each attachment and recreates registered sizes, simultaneously deleting old thumbnails that are no longer used by any theme or plugin.

In practice, this is the most reliable choice for a standard task: changed the theme, ran regeneration, got correct sizes. Nothing extra. Skips already correctly generated thumbnails, doesn't waste time on repeated work.

Pros:

• Maximally simple interface, anyone can figure it out
• Batch and individual regeneration from media library
• Built-in cleanup of unused thumbnail sizes
• Skips already correct thumbnails without regeneration

Cons:

• No forced regeneration, only creates missing sizes
• Doesn't support WP-CLI, for large media libraries the process goes through web interface
• Last tested on WordPress 6.8.5, slight lag from the current version

Price: free.

🔗 Regenerate Thumbnails on WordPress.org

2. Force Regenerate Thumbnails

A plugin by Shane Bishop that goes a step further than the classic Regenerate Thumbnails. Instead of creating missing sizes, it completely deletes all thumbnails for selected images and generates them anew. This is critical when old sizes physically lie on disk but are "crooked", which happens after changing several themes in a row or manually editing functions.php.

Version 2.3.0 from February 2026 added WP-CLI support: the wp force-regenerate-thumbnails command runs regeneration from the console without web server limitations. For sites with 50,000+ products in WooCommerce, this is the only way to avoid crashing the admin panel.

In practice: user koultti on WordPress.org describes a case with a site of 50,000 products, where after configuring sizes via Image Sizes Controller and converting to WebP, the plugin cleanly regenerated the entire media library without a single hang.

Pros:

• Complete deletion of old sizes before creating new ones, guaranteed clean result
• WP-CLI out of the box from version 2.3.0
• Resume interrupted process without losing progress
• Works with PDF thumbnails

Cons:

• Doesn't convert to WebP and AVIF, needs a separate plugin
• Deletes all sizes without the option to keep some, play it safe with a backup
• Less than 30 language locales

Price: free.

🔗 Force Regenerate Thumbnails on WordPress.org

3. reGenerate Thumbnails Advanced

A development by the ShortPixel team, creators of a popular image optimizer. The plugin is optimized for speed: the regeneration process runs with a progress bar and pause button, and if the connection drops, it automatically resumes from the same place.

The free version does exactly what it promises: regenerates thumbnails for all or selected images. You can set the quality of output thumbnails and add custom sizes on top of those registered by the theme. The Pro version for 59 dollars a year unlocks WP-CLI, automatic deletion of outdated thumbnails, and batch optimization launch via ShortPixel immediately after regeneration.

An important nuance: the plugin's last update was released in February 2024, which for the WordPress ecosystem looks like a freeze. However, 70,000+ active installations and work with WordPress 7.0 in practice show the tool is alive and performs the basic task. But for sites on the cutting edge of updates, it's better to look at Force Regenerate Thumbnails or Perfect Images.

Pros:

• Progress bar with completion percentage and pause button
• Auto-resume after disconnection, progress is not lost
• Integration with ShortPixel for compression after regeneration
• Output thumbnail quality settings

Cons:

• Old thumbnail cleanup and WP-CLI only in Pro for 59 USD per year
• Previously free features moved behind paywall, barrage of criticism in reviews
• Doesn't convert formats, only regeneration
• Last update February 2024, no new versions for over two years

Price: free / Pro from $59 per year.

🔗 reGenerate Thumbnails Advanced on WordPress.org

4. Perfect Images

A combine harvester from Jordy Meow, author of a dozen well-known WordPress plugins. Perfect Images combines three functions in one interface: thumbnail regeneration, conversion to WebP and AVIF, and management of all registered sizes. 278 reviews and 60,000+ active installations on WordPress.org.

The main difference from the rest, the plugin doesn't just recreate thumbnails, but gives full control over what sizes even exist on the site. See 15 registered sizes from different plugins? Disable unnecessary ones, leave 3-4 actually used and regenerate only them. On a test site with 2,000 images, cleanup from unused sizes alone freed 430 MB.

Retina mode generates double-resolution thumbnails for HiDPI screens. Conversion to WebP and AVIF goes either locally via Imagick/GD, or through a cloud service for an additional fee. Tested with WordPress 7.0, actively maintained.

Pros:

• Three in one: regeneration, size management, format conversion
• Disable unnecessary thumbnail sizes, radical disk cleanup
• Retina mode for HiDPI screens
• Actively maintained, tested with WordPress 7.0

Cons:

• More complex to configure than Regenerate Thumbnails, more parameters
• No forced regeneration, only standard
• Cloud optimization requires additional subscription

Price: free / Pro from $49 per year.

🔗 Perfect Images on WordPress.org

5. Simple Image Sizes

A plugin by Nicolas Juen with 60,000+ active installations that solves the task from a different angle. Instead of simply regenerating registered sizes, Simple Image Sizes first lets you redefine the sizes themselves right on the Settings → Media page.

Add new sizes, change proportions of existing ones, disable those registered by the theme but which you don't need, and only then launch regeneration. The result: you get exactly the sizes actually used in the layout, and not one more.

The plugin is especially useful when migrating to a custom theme where sizes are manually written via add_image_size() in functions.php. Instead of editing code, configure everything via admin panel and regenerate. Version 3.2.5, tested with WordPress 7.0, among the most compatible.

Pros:

• Direct thumbnail size management via admin panel
• Override theme sizes without editing functions.php
• Batch regeneration with progress indicator
• Tested with WordPress 7.0, stable

Cons:

• No forced regeneration
• No WP-CLI
• Minimalist interface, no visual frills

Price: free.

🔗 Simple Image Sizes on WordPress.org

6. Real Thumbnail Generator

A niche plugin from German studio devowl.io, created with emphasis on GDPR compatibility and SEO. Doesn't transmit image data to third-party servers, doesn't embed trackers, all processing is local. For European projects where compliance is critical, this is a weighty argument.

The interface is deliberately simple: select sizes, press Regenerate and watch the process. The plugin automatically detects registered sizes and shows only them, without extra noise. Built-in protection against duplication: if a thumbnail already exists in the correct size, it is not recreated.

Version 2.6.142, updated in May 2026, tested with WordPress 7.0. Despite a modest user base of around 1,000 active installations, the plugin is actively maintained and doesn't suffer from typical problems of abandoned tools.

Pros:

• Fully local processing, GDPR compatibility out of the box
• Auto-detection of registered thumbnail sizes
• Skips already correct thumbnails without regeneration
• Minimalist interface without ads and cross-promotion

Cons:

• Small user base, less coverage of edge cases
• No WP-CLI
• Only regeneration, without size management or format conversion

Price: free.

🔗 Real Thumbnail Generator on WordPress.org

Video: thumbnail regeneration in practice

If you prefer a visual demonstration, here's a step-by-step tutorial on thumbnail regeneration in WordPress:

⁉️🤔 Frequently asked questions

Will thumbnail regeneration delete original images?

No, none of the plugins in the collection touch the originals of uploaded files. Only derivative sizes are deleted and recreated, thumbnails, medium and large versions that WordPress generates on upload. The original always remains untouched in the uploads folder.

What's better: regeneration via plugin or WP-CLI?

WP-CLI works faster, doesn't run into web server timeouts and consumes fewer resources. The wp media regenerate command handles sites with 100,000+ images. But WP-CLI requires console access to the server, which may not be available on cheap hosting. Of the plugins, Force Regenerate Thumbnails and reGenerate Thumbnails Advanced Pro support WP-CLI out of the box, for the rest, only web interface.

Do I need to make a backup before regeneration?

Absolutely. Regeneration physically overwrites files on disk. A process interrupted in the middle leaves some thumbnails in the old size, some without thumbnails at all, you get visual chaos on the site. Full backup of files and database before launch, a rule we follow even on test stands.

The regeneration plugin is slow or hangs, what to do?

Three steps: increase max_execution_time in php.ini to 300 seconds, raise memory_limit to 256M and run regeneration in batches, by post types or upload dates, not for all images at once. If the site is on WooCommerce with tens of thousands of products, only WP-CLI: the web interface of any plugin will choke on such volumes.

Can I regenerate thumbnails selectively, only for WooCommerce products?

Yes, practically all plugins in the collection allow filtering images by post type. Regenerate Thumbnails and Force Regenerate Thumbnails show which posts each image is attached to and let you selectively run regeneration only for product images. reGenerate Thumbnails Advanced Pro adds a filter by date ranges, convenient for fresh arrivals.

What to install in 2026

Changing themes and need to bring thumbnails in order once, take Regenerate Thumbnails, a classic won't let you down. Old sizes physically clutter the disk and you need a complete cleanup, Force Regenerate Thumbnails with its forced deletion and WP-CLI out of the box. Want WebP with AVIF on output as well, Perfect Images does everything in one interface. Need control over the sizes themselves and not just their recreation, Simple Image Sizes. European project with GDPR, Real Thumbnail Generator.

Before launch, backup. After regeneration, check the storefront and galleries for broken images. And don't forget to clear cache: server, browser and CDN, otherwise you'll see old sizes and decide the plugin didn't work.